1. Field of the Invention
This invention relates to an electromagnetic clutch for transmitting and cutting-off turning power. The invention is suitable for connecting and cutting-off a compressor operation, for a car air conditioner, for example.
2. Description of the Related Art
An electromagnetic clutch for a compressor of a car air conditioner according to the prior art includes a rotor driven and rotated by a driving source such as an engine and an armature so disposed as to face the rotor with a predetermined small clearance between them. A hub structure of a leaf spring type is known as one of the hub structures for interconnecting the armature to a rotary shaft on the compressor side. In this hub structure, one of the ends of a leaf spring is interconnected to an inner hub that is in turn interconnected to the rotary shaft on the compressor side and the other end of the leaf spring is interconnected to the armature.
Because the hub structure of the leaf spring type can use an economical iron type material as a leaf spring material and can also use simple interconnecting means such as rivet coupling for the interconnecting portion of the leaf spring, this hub structure has the advantages that the manufacturing cost can be reduced and the size of the electromagnetic clutch in an axial direction can be reduced. However, it is known that, because the power transmission system from the armature to the hub does not have a damping mechanism of vibration (impact) and torque fluctuation, the hub structure cannot provide a damping effect regarding a clutch operation sound and torsional resonance.
In the construction of the existing electromagnetic clutches, frictional surfaces, of the armature and the rotor and that are made of iron, directly impinge against each other. Therefore, there remain the problems that the transmission torque increases with the increase of the number of times of connection/disconnection from the relation of compatibility of the materials besides the occurrence of the operation sound, and the initial transmission torque is lower than the transmission torque after connection/disconnection.
Another problem is that surface treatment is necessary because the raw material of both plate (leaf spring) and armature is iron.
To cope with the problems, Japanese Unexamined Patent Publication No. 2000-161389 as a prior art reference reduces the operation sound by directly interconnecting the leaf spring member (plate) and the armature through an elastic member made of rubber.
According to this prior art technology, too, the problem yet remains unsolved that the surface treatment is necessary because the leaf spring member (plate) is exposed. Another problem is that reaction becomes high and an operation factor is deteriorated because the spring portion of the leaf spring member is bonded to the elastic member.
Furthermore, the problem of the impingement sound that occurs when electric power is fed to the electromagnetic coil and the armature is attracted to the rotor is not solved, either, because the armature is so disposed as to face the rotor with a clearance between them. Further, the problem also remains that when the armature is operated, the leaf spring member vibrates and noise occurs.